The present invention relates to coating compositions or lacquers and to molding compositions with a polysiloxane content which produces anti-adhesive characteristics and which increases the lubricity. Further, the invention relates to the use of certain defined polysiloxanes as described hereinafter to produce anti-adhesive characteristics in lacquers and molding compositions.
It is known to add polysiloxanes to coating compositions or lacquers in order to obtain a soil-resistant surface by means of the resulting boundary layer. Additionally, the scratch resistance and lubricity of the surfaces are improved by such polysiloxane additions.
Polysiloxanes are also added to molding compositions in order to facilitate release of formed articles from the molds following a molding process involving a chemical cross-linking reaction under the influence of elevated temperatures.
The aforementioned characteristic of forming antiadhesive surface layers is of particular interest with regard to surfaces which might be expected to be soiled or defaced, for example, in cases of vandalism where grafitti is applied to the facades of buildings by spraying spray paint on them. Facades which are protected with anti-adhesive products can be easily cleaned again.
By using a polysiloxane in paints or lacquers, furniture surfaces are also made more scratch resistant, so that the visible results of abrasions which occur during daily use, such as scratches and markings, can be clearly reduced.
Polysiloxane modified binders are also used in coating papers which exhibit the known anti-adhesive action of so-called release papers.
For the aforedescribed purposes, polysiloxanes from the classes of dimethylpolysiloxanes, methylphenylsiloxanes, polyalkylene-modified dimethylpolysiloxanes, reactive polydimethylpolysiloxanes, and hydroxy-functional polyethersiloxanes are used. The use of these products is described in West German Pat. Nos. 11 11 320 and 10 92 585, published European Patent Application Nos. 116,966 and 103,367, U.S. Pat. No. 4,076,695, and in Proceedings of the SPI, 6th International Technical Conference--Improved RIM-Processing with Silicone Internal Mold Release Technology, as well as in the brochure "Goldschmidt Informiert" (Goldsmith Informs), July 1982, No. 56, page 2, and in Fatipec Congress Book, 1963, page 332.
A surface activity is ascribed to each of these aforementioned polysiloxanes which manifests itself in an enrichment of these polysiloxanes occurring at the liquid/gas or solid/gas boundary surface so that the desired characteristics are produced, i.e. a reduction of adhesion and an increase in lubricity.
Silicon-modified binders constitute a separate class of coating compositions which cannot be compared to the aforedescribed polysiloxanes since in silicon-modified binders the polysiloxane groups are fixedly incorporated into the binder by polyaddition and polycondensation. These silicon resins substantially fulfill the requirements placed on them for anti-adhesive characteristics, but because of the high Si-content, they are very expensive, and therefore they can only be used to a limited extent.
With the exception of reactive polysiloxanes, these polysiloxane structures are inert substances with regard to their reactivity with the lacquers and molding compositions. The results achieved with them in reducing the adhesion or increasing the lubricity are consequently not of long enduring effectiveness, for because of the surface orientation, these polysiloxanes can be easily wiped away or washed away with solvents, whereby the effect is lost.
Polysiloxanes which carry reactive functional groups are, because of their incompatibility, very difficult to incorporate into lacquers or molding compositions, since they tend to separate and are not homogeneously distributed throughout the reaction system during the reaction of the lacquer binder resin or molding composition resin with itself and are only partially incorporated into the product. Attempts have been made to avoid this by incorporating such reactive polysiloxanes into the reactive resin during its production. However, the mobility of the polysiloxanes is adversely affected thereby, and orientation toward the surface is substantially prevented, so that relatively large amounts of polysiloxane must be utilized in order to achieve the desired anti-adhesive effect.
Use of carboxy-functional siloxanes according to U.S. Pat. No. 4,076,695 in polyurethane systems delays the urethane-forming reaction so that a sufficiently rapid reaction is not achieved without a drastic increase in the catalyst proportion or a modification of the processing procedure. Because of the incompatibility of polysiloxanes of the types described in U.S. Pat. No. 4,076,695, published European Patent Application No. 103,367 and published European Patent Application No. 116,966, disruptions of the cell structure may arise during foaming, particularly in polyurethane foams, which leads to irregularities in structure.
Polyether-modified polysiloxanes have only limited temperature stability when subjected to the influence of oxygen because of the polyether structure, so that a breakdown of the polyether chain arises at temperatures above 150.degree. C. which leads to disturbances in the lacquer resin or the molding composition.